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08 September 2012

Hunger - The Role of Insulin

The classic approach to weight loss is to eat less, so researchers put obese patients on a calorie-restricted diet. If they loose weight, it means that obesity is caused by overeating. The problem is that results are not really compelling. The subjects usually loose weight, but the diet results in negative physiological effects as well, such as:

Slow nail growth

Hair fall

Wounds bleed less, and take more time to heal

Pulse rates were reduced

Depression, loss of ambition

Constant feeling of cold

Constant feeling of hunger

When the subjects returned to a normal diet, many of them weighed more than at the start of the experiment.

Calorie restriction is a state of chronic undernourishment, it might result in weight loss, but also in the loss of all body tissue.

If constant hunger is experienced and the subject regain at least the initial weight at the end of the experiment, it means that these semi-starvation diets are not the long-term answer to weight loss. As the Handbook of Obesity (George Bray, Claude Bouchard and W.P.T. James, 1998) says: the results of calorie-restricted diets "are known to be poor and not long-lasting". To this day, this does not prevent health authorities from recommending to eat less.

Some researchers believed that the hormone insulin has a lot to do with weight gain. When comparing calorie-restricted diets with low-carbohydrate diets (not restricted in calories), both resulted in weight loss, but the subjects on the low-carbohydrate diet were not experiencing the negative effects of semi-starvation and their overall health was better than on the calorie-restricted diet.

When patients were put on a high-fat diet:

"Without exception, the low-carbohydrate reducing diet resulted in satisfactory weight losses. [...] The subjects reported a feeling of well-being and satisfaction. Hunger between meals was not a problem."
- Margaret Ohlson

It is also interesting to note that when the subjects were put on a high-fat, but calorie-restricted diet of for example 1,200 calories/day (Willard Krehl, University of Iowa, 1967), subjects still reported a lack of hunger. The same weight-loss results were reported on subjects on a high-fat, eat-as-much-as-you-want diet.

"[...] Per Hanssen in 1936 suggested that the 1,800-calorie carbohydrate-restricted diet was likely to make weight maintenance easier than a 900-calorie balanced diet."
- Gary Taubes

(A "balanced diet" includes carbohydrates.)

When investigators compared a high-fat eat-as-much-as-you-want diet with a high-carbohydrate eat-as-much-as-you-want diet, they found that it was difficult to convince the subjects on the high-fat diet to overeat even by 1,000 calories. Satiety was reached very easily. However, subjects on the high-carbohydrate diet overate very easily, adding even 3,000 calories to the daily requirement of 2,700 calories. The results showed weight gain on the high-carbohydrate diet, and weight maintenance or weight loss on the high fat diet.

When Ethan Sims stuffed his subject with 10,000 calories per day, including carbohydrates, they reported feeling "hunger late in the day".

If this is the case that there's no feeling of hunger and weight loss is maintained on a high-fat diet (even when calories are not restricted), and hunger is almost constant on a diet high in carbohydrates, then it's a reasonable assumption that insulin plays a role in the feeling of hunger (as insulin levels increase on a high-carbohydrate diet).

Now, let's see a bit of biochemistry.

When our organs receive the required energy (fatty acids) to function, we don't have a feeling of hunger. Once these fatty acids are depleted from our bloodstream, we are hungry. So anything that takes out fatty acids from the bloodstream:

Exercise: we burn fatty acids. After a few hours in the gym, we feel hungry.

Carbohydrates: by elevating insulin levels and storing the fatty acids in our adipose tissues, we feel hunger. The fatty acids go to storage instead of fueling our organs and muscles. Our body cannot see the storage of fat, and our brain tells us to eat more. Insulin prevents the release of fatty acids from the fat tissues into the bloodstream. "The use of fat for fuel is suppressed." (- Gary Taubes).

Anything that lowers insulin levels, and thus makes the fatty acids available for fuel, suppresses hunger. A diet high in fat will result in very low insulin levels, so the fatty acids will circulate freely in our blood and will be used by the cells of the organs in need of fuel.

"As long as we respond to the carbohydrates by secreting more insulin, we continue to remove nutrients from our bloodstream in expectation of the arrival of more, so we remain hungry [...]."
- Gary Taubes

You can try a little experiment yourself. It is very easy to gobble up a big bag of popcorn or cookies (carbohydrates). Now try to eat, the equivalent in calories of one and a half cup of melted cheese (fat). Which food is more satisfying and suppresses hunger for a longer period of time?